This invention relates to a fluid displacement apparatus, and in particular, a fluid compressor unit of the scroll type.
Scroll type apparatus are well known in the prior art. For example, U.S. Pat. No. 801,182 discloses a scroll type apparatus including two scroll members each having an end plate and a spiroidal or involute spiral element. These scroll members are maintained angularly and radially offset so that both spiral elements interfit to make a plurality of line contacts between spiral curved surfaces, thereby sealing off and defining at least one pair of fluid pockets. The relative orbital motion of the two scroll members shifts the line contacts along the spiral curved surfaces to change the volume of the fluid pockets. The volume of the fluid pockets increases or decreases dependent on the direction of the orbiting motion. Therefore, this scroll type apparatus can be used to compress, expand or pump fluids.
In comparison with conventional compressors of the piston type, the scroll type compressor has certain advantages, such as a fewer parts and continuous compression of fluid. However, one of the problems with scroll type compressors is the ineffective sealing of the fluid pockets. Axial and radial sealing of the fluid pockets must be maintained in a scroll type fluid displacement apparatus in order to achieve efficient operation. The fluid pockets are defined by the line contacts between two interfitting spiral elements and axial contacts are defined by the axial end surface of one spiral element and the inner end surface of the end plate of the other spiral element.
Various techniques have been used in the prior art to resolve the sealing problem, particularly, the axial sealing problem. For example, U.S. Pat. No. 3,924,977 discloses a technique for non-rotatably supporting the fixed scroll member within the compressor housing in an axially floating condition. A high pressure fluid is introduced behind the fixed scroll member to establish sufficient axial sealing. In this technique, since the fixed scroll member is supported in an axially floating condition, the fixed scroll member may wobble due to the eccentric orbital motion of the orbiting scroll member. Therefore, sealing and resultant fluid compression tends to be imperfectly performed.
In order to avoid these disadvantages, the pressure of the high pressure fluid must be increased and the clearance between radial supporting parts must be made as small as possible. However, minimizing the clearance is expensive due to the close tolerance requirements, while an increase in pressure increases contact pressure between both scroll members, which increases mechanical loss or causes damage to the scroll members.
Another technique for improving the axial seal of the fluid pockets is to use sealing elements mounted in the axial end surface of the each spiral elements, as disclosed in U.S. Pat. No. 3,994,635. In this technique, the end surface of each spiral element facing the end plate of the other scroll member is provided with a groove formed along the spiral. A seal element is placed within the grooves and an axial force urging device, such as a spring, is placed behind the seal element to urge the seal toward the facing end surface of the end plate to thereby effect axial sealing. In this technique, the construction of the axial force urging device is complex and it is difficult to obtain the desired uniform sealing force along the entire length of the seal element.
In order to avoid these disadvantages, the seal element is loosely fitted into the groove in the axial end surface of each spiral element. As a substitute for a mechanical axial force urging device, the pressurized fluid then is introduced into the groove from adjacent fluid pockets to urge the seal element towards the facing end plate to thereby effect axial sealing. However, the seal element is subject to localized excessive wear during a portion of the orbital motion of the orbiting scroll member. That is, during the period when the pair of fluid pockets are both connected to the center high pressure space, localized fluid pressure behind the seal element is suddenly enlarged, resulting in excessive sealing force which sometimes induces localized bending of the seal element and excessive sealing force. Also, the groove in which the seal element is disposed extends from the center of the spiral element to near the terminal end thereof. Therefore, high pressure fluid flows into the groove and leaks into low pressure spaces along the groove to reduce the volumetric efficiency of the compressor.